URGENT: My first video recording - tonight!

My wife is part of an amateur orchestra. There's always an "end of term" performance, and it's tonight.

The lady who founded and for many years has continued to run the orchestra has been taken to hospital yesterday. She is seriously - possibly terminally - ill.

We want to video tonight's performance so she can view it in hospital (or, we hope, at home). I have never done a video of anything much. It won't need to be professional and polished, but obviously I'd like to avoid any stupid mistakes and do as good a job as I can.

The performance will be in a large-ish room at a local hall. It will not be particularly well lit. It's a mix of full orchestra (~30 people) and smaller pieces (1-4 people).

I'll be using the E-M1 (unless there's some reason to go with the E-Pl7) but not sure what lens I should use - the 12-40mm is probably best>?